U.S. patent application number 12/739632 was filed with the patent office on 2012-11-08 for method of determining the particle sensitivity of electronic components.
This patent application is currently assigned to AIRBUS FRANCE. Invention is credited to Nadine Buard, Thierry Carriere, Patrick Heins, Florent Miller, Cecile Weulersse.
Application Number | 20120284006 12/739632 |
Document ID | / |
Family ID | 39535832 |
Filed Date | 2012-11-08 |
United States Patent
Application |
20120284006 |
Kind Code |
A1 |
Miller; Florent ; et
al. |
November 8, 2012 |
METHOD OF DETERMINING THE PARTICLE SENSITIVITY OF ELECTRONIC
COMPONENTS
Abstract
To analyze an electronic component, this component is exposed to
a focused laser beam. The information provided by the laser mapping
relating to the position and to the depth of the sensitivity zones
of the component is used as input parameter in prediction codes for
quantifying the sensitivity of the mapped component to ionizing
particles in the natural radioactive environment. The prediction
codes are used to determine the occurrence of malfunctions in the
electronic component. Determination of the risks associated with
the radiative environment imposes two aspects: one, probabilistic,
takes into account the particle/matter interaction and the other,
electrical, takes into account the charge collection inside the
electronic component.
Inventors: |
Miller; Florent; (Levallois,
FR) ; Buard; Nadine; (Meudon, FR) ; Weulersse;
Cecile; (Versailles, FR) ; Carriere; Thierry;
(Triel Sur Seine, FR) ; Heins; Patrick; (Castelnau
de Montmiral, FR) |
Assignee: |
AIRBUS FRANCE
Toulouse
FR
EUROPEAN AERONAUTIC DEFENCE AND SPACE COMPANY EADS
FRANCE
PARIS
FR
ASTRIUM SAS
Paris
FR
|
Family ID: |
39535832 |
Appl. No.: |
12/739632 |
Filed: |
October 23, 2008 |
PCT Filed: |
October 23, 2008 |
PCT NO: |
PCT/FR08/51913 |
371 Date: |
July 12, 2010 |
Current U.S.
Class: |
703/13 |
Current CPC
Class: |
G01R 31/318357 20130101;
G01R 31/2849 20130101; G01R 31/308 20130101; G01R 31/2881 20130101;
G01R 31/002 20130101; G01R 31/31816 20130101 |
Class at
Publication: |
703/13 |
International
Class: |
G06G 7/62 20060101
G06G007/62 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 26, 2007 |
FR |
07 58621 |
Claims
1. Method for characterising the sensitivity to energy interactions
of an electronic component in which: the electronic component is
put into operation, the electronic component thus put into
operation is excited by excitations produced by a laser radiation,
a malfunction of the electronic component put into operation,
corresponding to these excitations, is measured, a mapping is made
of the sensitivity zones of the component in which these
excitations have an effect, a program of simulation of stress
applied by a particle prompting energy interactions is applied to
the mapping of the sensitivity zones, this simulation program
produces a large number of possible paths taken by the particles in
the component and, in the case of a neutrons and protons, a large
number of reactions extracted from a data base, this simulation
program implements a charge collection model from these possible
paths and from the mapping of the sensitivity of the component,
this simulation program analyzes these charge collections and
decides on the occurrence of errors related to these charge
collections, the quality signal of the component is deduced from
this analysis and from these decisions.
2. Method according to claim 1, wherein a data base is used, in the
case of the neutrons and the protons, providing information on
products and probabilities of possible nuclear reactions, and the
effect of the ionization on the working of the components is
measured.
3. Method according to claim 2, wherein a processing is applied to
the prepared laser mapping to extract a useful mapping, this useful
mapping taking account of the sensitivity of the component to the
ionizing particles.
4. Method according to claim 3, wherein a mathematical
deconvolution is performed to take into consideration a size of a
laser impact relative to an estimated size of a zone of sensitivity
of the component to ionizing particles.
5. Method according to claim 4, wherein for components with fine
integration, a maximum size of the zone of sensitivity of an
elementary cell is measured with the laser mapping.
6. Method according to claim 5, wherein to quantify the sensitivity
of the component, a response is measured of the electronic
component to excitations according to criteria determined for the
dysfunction studied.
7. Method according to claim 6, wherein the simulation program
chooses nuclear reactions from a data base corresponding to the
type and energy of the particle studied.
8. Method according to claim 7, wherein as a measurement of energy
interaction, interactions of heavy ions and/or of protons and/or of
neutrons are measured by laser simulation.
9. Method according to claim 8, wherein the energy of the laser
photon of the laser source is greater than the value of the bandgap
of the semiconductor component.
10. Method according to claim 9, wherein the laser source prompts a
simultaneous absorption of several photons in the semiconductor
material.
11. Method according to claim 10, wherein the laser mapping is done
in all three dimensions of space.
12. Method according to claim 11, wherein the laser mapping is done
in four dimensions, the three dimensions of space ainsi as well as
time.
13. Device for implementing the method according to claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is the National Stage of International
Application No. PCT/FR2008/051913 International Filing Date, 23
Oct. 2008, which designated the United States of America, and which
International Application was published under PCT Article 21 (s) as
WO Publication No. WO2009/056738 A1 and which claims priority from,
and the benefit of, French Application No. 200758621 filed on 26
Oct. 2007, the disclosures of which are incorporated herein by
reference in their entireties.
[0002] The aim of the aspects of the disclosed embodiments is to
determine the sensitivity of electronic components to particles
such as heavy ions, neutrons and protons through the joint use of a
laser system and a malfunction prediction code based on the physics
of particle/matter interaction.
BACKGROUND
[0003] Natural or artificial radiative environments (with neutrons,
protons, heavy ions, flash x-rays, gamma rays) can disturb the
working of electronic components. These disturbances are due to
interaction between matter and the particles of the radiative
environment. One consequence is the creation of parasitic currents
in the component. The magnitude of the parasitic currents produced
will vary according to the interactions between matter and
particles. This results in the presence of localized charge
collection areas in the component.
[0004] Such stresses created by heavy ions and protons are
typically encountered in space by satellites and launchers. At
lower altitudes in which aircraft move, stresses especially from
neutrons can be noted. Such stresses may be encountered at sea
level too and may affect electronic components embedded in portable
apparatuses or in automobiles.
[0005] To be able to predict the behavior of components with
respect to heavy ions, neutrons and protons especially for space
and aeronautical applications, it is necessary to know the surface
area of the charge accumulation zones as well as their position and
dimension in depth. This presupposes the ability to create 3D
mapping.
[0006] Classically, to assess the particle sensitivity of an
electronic component to the particles of the radiative environment,
the component is subjected to a stream of particles and the
disturbances are accounted for. Inasmuch as the entire component is
irradiated, this type of test does not allow for tracing back to
the location of the charge collection zones. Furthermore, these
tests are relatively costly because there are relatively few
installations in the world capable of producing streams of
particles. Finally, even if the nature of the particles coming from
the particle accelerators is the same as that of the radiative
environment, their energy may be different. This may lead to major
errors, especially because of their lesser penetration into the
component.
[0007] Small-sized beams may be extracted from the output of the
particle accelerator. These microbeams can therefore be used to map
the zones of sensitivity of a component. This mapping is done in a
plane and reveals the location of the charge collection zones only
superficially. No information on the location of the sensitive zone
in depth is obtained by this type of test.
[0008] Until now, laser has been used chiefly as a tool for
pre-characterising the sensitivity of the components to radiation.
Just as with the particles of the radiative environment, laser can
generate parasitic currents within the components when its
wavelength is appropriate.
[0009] Laser has a very valuable advantage for studying the effect
of radiation. Since the spatial resolution of a laser can reach
relatively small dimensions as compared with the elementary
structures contained in electronic components, it is possible, as
in the case of a microbeam, to map an electronic component and
identify its charge collection zones. By varying the focusing point
of the beam in depth, it possible to map sensitivity in the third
dimension too, and this can easily be done on an industrial scale.
However, this knowledge is not sufficient to know the overall
behavior of the electronic component under radiation.
SUMMARY
[0010] To overcome this problem, the disclosed embodiments have
come up with the idea of working by simulation. Once the map of
sensitivity of the component has been acquired, it is presented in
the form of a model, in practice a matrix, having four or five
dimensions, in an X Y Z referential frame with a coefficient of
sensitivity or in an X Y Z T referential frame with a coefficient
of sensitivity. This model of the component is then subjected to
simulated stress and its simulated response is measured. For
example schematically, if at a given instant T, a simulated ion
(whether it is a primary ion or an ion produced by a nuclear
reaction) passes through an elementary zone having X Y Z
co-ordinates and, if at this instant, the elementary zone concerned
has a sensitivity s, the zone is assigned the value of quality s.
Then, this experiment is reiterated for another simulated ion. The
process is continued in this way over a given period of study
while, if the time varies as the case may be and if the application
put into operation by the component runs on, the values s are
collected and then for example at the end of a given period of
measurement, the measured values of quality are compiled in order
to find out the real quality of the component. Through this mode of
action, a true measurement of quality is obtained rather than a
mapping that is subject to conjecture.
[0011] According to the disclosed embodiments, the knowledge given
by the laser mapping operations on the position and depth of the
zones of sensitivity of an electronic component can be used as
input parameters in prediction codes to quantify the sensitivity of
the mapped electronic component to ionizing particles of the
natural radiative environment. The prediction codes enable an
assessment of the occurrence of malfunctioning in an electronic
component. The assessment of risks related to the radiating
environment dictates two aspects: the first aspect, which is
probabilistic, takes account of a particle/matter interaction. The
other aspect which is electrical takes account of the collection of
charges within the electronic component.
[0012] This method is used to determine the sensitivity of
electronic components to radiation through laser tests: the
information on the geometry of the charge collection zones of the
component then serve as input parameters in simulations of error
prediction relative to the particles (heavy ions, neutrons, protons
etc). The method of the disclosed embodiments highlights the
weaknesses of a particular technology to radiation resistance. This
is a major piece of information in developing new components from
the viewpoint of manufacturing methods and for the choice of
electronic components to be used in electronic systems so that they
have the lowest sensitivity. In the disclosed embodiments, in the
case of a study of sensitivity to neutrons or protons, rather than
carrying out exhaustive simulations of nuclear reactions with the
constituent nuclei of the electronic components, it is preferred to
use a preliminarily built data base which, for an energy of stress
from a given incident particle gives the characteristics of the
products coming from the reactions as well as the probabilities
associated with each of the possible reactions. In the case of
heavy ions, the nuclear reactions are not studied and there is no
data base because the heavy ions directly have high ionizing
capacity. The simulation code enables the assessment, from
criteria, of the effect that the interaction of these particles
would have had on the working of the electronic component.
[0013] An aspect of the disclosed embodiments therefore is a method
for characterising sensitivity to energy interactions of an
electronic component in which: [0014] the electronic component is
put into operation, [0015] the electronic component thus put into
operation is excited by excitations produced by a laser radiation,
[0016] a malfunction of the electronic component put into
operation, corresponding to these excitations, is measured, [0017]
a mapping is made of the sensitivity zones of the component in
which these excitations have an effect, [0018] a program of
simulation of stress applied by a particle prompting energy
interactions is applied to the mapping of the sensitivity zones,
[0019] this simulation program quantifies the sensitivity of the
component on the basis of a large number of possible paths taken by
the particles in the component and in the case of a neutrons and
protons of a large number of reactions extracted from a data
base.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The disclosed embodiments will be understood more clearly
from the following description and the accompanying figures. These
figures are given purely by way of an indication and in no way
restrict the scope of the disclosed embodiments. Of these
figures:
[0021] FIGS. 1a to 1c show three different cases of study for
distinguishing the efficiency of the attack following a level of
integration of the components;
[0022] FIG. 2 shows the symbolic content of a data base which gives
a detailed description of the products created during a nuclear
reaction for an incident particle of given energy and the
probability associated with this reaction;
[0023] FIG. 3 shows the general principle of a Monte-Carlo code for
predicting the sensitivity of electronic components;
[0024] FIGS. 4a and 4b provide a time-based representation of the
collection of carriers deposited by the passage of an ion and the
principle of a criterion (Imax, tImax) of SEU for a 0.6 .mu.m
technology.
DETAILED DESCRIPTION
[0025] According to the disclosed embodiments, a laser device makes
it possible first of all to place an electronic component to be
tested into operation, excite it by excitations produced by a laser
ray and measure a malfunction of the electronic component put into
operation corresponding to these excitations. This device thus
makes it possible to set up a mapping of sensitivity zones of the
component where these excitations have an effect. In one example,
the laser source prompts an absorption of protons in the
semiconductive material of the component.
[0026] The aspects of the disclosed embodiments are then based on
the joint use of a laser system and a prediction code to compute
the sensitivity of an electronic component to the natural radiating
environment. The laser is used to map the sensitivity of the
component to the localized injection of charges. A criterion is
observed. This criterion takes account of the event studied. It can
be an electrical signal which, when the event is activated, is
different from the expected signal. In the case of a logic
component such as a memory, it may be the value stored in a memory
cell. For a linear component, it may be an analog signal of the
component.
[0027] The system comprises: [0028] a laser source the wavelength
of which enables the generation of charges in the semiconductive
material considered (by a mechanism of linear or non-linear
absorption); [0029] a device for the relative shifting of the laser
relative to the component being tested along all three directions
of space; [0030] possibly, an interface enabling communications
between the component being tested and the system for controlling
the laser [0031] a system for modifying laser energy; [0032] a
system to ascertain that an event has or has not taken place.
[0033] A mapping of sensitivity of the component is performed in
all three dimensions of space. It can also take account of time,
thus adding another dimension. For each position, X Y Z of the
mapping system and, as the case may be, for each instant t of the
cycle of operation of the component or of the application executed
by this component, a laser shot is made. This laser shot prompts
the generation of charges within the semiconductor material. Under
the influence especially of electrical fields and diffusion
mechanisms, the charges start moving and create currents which can
disturb the working of the electronic component. Not all the
positions (spatial and temporal positions) of the mapping system
will have the same sensitivity because spatially the physical
parameters of the component are not the same depending on the
position and, temporally, not all the zones of the component are
acted upon in the same way in the course of time. Laser mapping
makes it possible to highlight the zones of sensitivity of a
component under localized generation of charges, i.e. to reveal
variations in spatial sensitivity and possibly temporal
sensitivity. These are zones sensitive to ionizing particles
(directly or indirectly ionizing particles) such as heavy ions,
neutrons and protons.
[0034] Laser mapping is used to identify:
[0035] 1--the spatial position X Y Z of a zone of sensitivity;
[0036] 2--the temporal position of a zone of sensitivity, i.e. the
points in time at which a zone is seen to be sensitive to the
injection of charges;
[0037] 3--the shape and volume of this zone of sensitivity (which
evolves as the case may be as a function of time);
[0038] 4--the relative position of the zone of sensitivity relative
to neighboring zones of sensitivity;
[0039] 5--in the case of logic components and if necessary the
logic function impacted during an injection of charges into the
zone of sensitivity.
[0040] The pieces of information 4 and 5 extracted from the laser
mapping depend on the technology, the conditions of use, as the
case may be the application operated by the component. On the
contrary, they do not depend on the rate at which the charges are
deposited and are therefore valid whatever the charge deposit
considered (whether particles or laser charge for example). The
pieces of information 1, 2 and 3 extracted from the laser mapping
process depend on the technology, the conditions of us and, as the
case may be, the application made by the component. They also
depend on the temporal rate (for 2) and spatial rate (for 1 and 3)
of the charge deposit. In the case of 2, there are lasers having
equivalent pulse durations equivalent to the duration of the
deposit of charges of an ionizing particle in a semiconductor
material (close to one picosecond) and in this case the information
obtained is valid whatever the charge deposit considered (particles
or laser for example).
[0041] Thus, the laser mapping makes it possible to obtain two
different types of information. In the former case, laser mapping
can be directly exploited to extract data on the sensitivity of the
electronic components relative to particles of the radiation
environment, in the cases 4 and 5.
[0042] In the second case, cases 1, 2 and 3, it is necessary to
apply processing to the laser mapping to extract payload
information to estimate the sensitivity of the electronic
components relative to the particles, and this processing takes
account of the specific nature of the particle/matter
interaction.
[0043] With regard to the direct exploitation of laser mapping,
namely cases 4 and 5, laser means can be used to identify the
relative positions of the zones of sensitivity (and depending or
not depending on time). The precision of this piece of information
is not linked to the size of the spot but to the size of the pitch
of movement used to obtain the laser mapping. In this sense,
obtaining this piece of information on distance between sensitive
zones is independent of the size of the beam considered.
[0044] For the most integrated components possessing a very fine
periodic arrangement of elementary cells (such as memories), the
geometrical information on distance between a cell and its nearest
neighbors obtained through laser mapping also gives the maximum
size of the zone of sensitivity of an elementary cell (since the
entire cell is seen as being sensitive). This piece of information
is obtained directly and can be exploited without processing.
[0045] As regards the processing of laser mapping, in the second
case identified, namely 1, 2 and 3, it is necessary to apply
processing to laser mapping to extract payload information to
estimate the sensitivity of the electronic components relative to
the particles of the radiating environment. It is then necessary to
distinguish between three different cases of studies depending on
the level of integration of the component. These three cases are
explained with reference to FIGS. 1a to 1c.
[0046] Case A: Less-integrated components for which the ionization
trace of the laser and the ionization trace of a given energy ion
have a size smaller than the characteristic dimensions of the
elementary structures and/or the zones of sensitivity of the
electronic component.
[0047] Case B: Integrated components for which the ionization trace
of the laser is of a size greater than that of the characteristic
dimensions of the elementary structures or the zones of sensitivity
of the electronic component while the trace of ionization of a
given energy ion is small-sized as compared with these
structures.
[0048] Case C: Highly integrated components for which the
ionization trace of the laser and the ionization trace of a given
energy ion are of a size greater than the characteristic dimensions
of the elementary structures or the zones of sensitivity of the
electronic component.
[0049] In each of the cases, it is possible to process the data in
order to know the zone of sensitivity relative to the ionizing
particles (whether direct or indirect ionization).
[0050] In the first case A, the charge deposit obtained by a
focused laser and the charge deposit obtained by an ion are highly
localized relative to the elementary structures of the component.
The zones identified as being sensitive by the laser will be also
sensitive for the ions. The laser mapping therefore makes it
possible in this case to directly identify spatially and/or
temporally the zones that are sensitive to the passage of an
ionizing particle (directly or indirectly).
[0051] In the second case B, the laser will over-estimate the size
of the zone of sensitivity as compared with what was already
detected as being sensitive by an ion. In other words, the zone of
sensitivity detected by the laser appears to be a convolution of
the real zone of sensitivity of the component with the size of the
ionization trace generated by the laser. We then proceed to a
mathematical de-convolution which is used to take the size of the
laser spot into consideration for the extraction, from a laser
mapping, of the estimated size of the zone of sensitivity of the
component relative to ionizing particles. The mathematical
de-convolution is an operation for retrieving the real zone of
sensitivity of the component where the zone of sensitivity detected
by the laser and the shape and size of the ionization trace of the
laser are known. From the mathematical viewpoint, this can be
expressed by the resolution of the following equation:
ZSlaser=f(ZSi)
[0052] where: ZSlaser is the zone of sensitivity identified by the
laser, ZSi is the zone of sensitivity of the component relative to
the particles and f is a function of the ionization trace of the
laser.
[0053] The resolving of the equation consists in finding the
function so f-1 that: ZSi=f-1 (ZSlaser) can be determined.
[0054] In the third case C, whether the deposit of charges is due
to an ion or to a laser, its size is greater than the size of the
elementary structure of the component. From the viewpoint of this
elementary structure, the charge deposit due to an ion or to a
laser is almost the same because the charges are created throughout
the elementary structure. In this case, it is easy to make the
correlation in order pass from information on sensitivity obtained
by laser to expected information on sensitivity relative to
ionizing particles since the entire elementary structure in this
case is sensitive. The zones of sensitivity associated with the
elementary structures and detected by laser and by ion are directly
linked to the size of the ionizing traces of the laser and of the
ion respectively.
[0055] The localizing of the sensitivity zones in depth is
determined by causing the focusing point of the laser beam to vary
either by changing the focal length or by shifting the focused
laser in depth relative to the component.
[0056] Thus, the laser makes it possible to send back geometrical
information on the position and size of the zones of sensitivity of
the electronic components relative to ionizing particles. As the
case may be, in case B, there will be withdrawal or no withdrawal.
Subsequently, to quantify the sensitivity of the electronic
components relative to ionizing particles, it is necessary to
couple these pieces of geometrical information with a prediction
code as described further below.
[0057] In order to assess the sensitivity of a given electronic
component in a given radiation environment (space or avionic
environment), many prediction tools have been developed, among them
SMC DASIE (Simplified Monte-Carlo Detailed Analysis of Secondary
Ion Effects). This method has been described in G. Hubert et al "A
review of DASIE codes family: contribution to SEU/MBU
understanding" in "11th IEEE International On-Line Testing
Symposium", 2005. The various versions of this code are based on
the same principle of exploitation of nuclear data bases coupled
with charge collection modules and criteria for activating effects.
The laser enables the extraction of data on method and sensitivity
through localized injection of charges for a particular component
with a technology unknown at the outset. These Monte-Carlo
computation tools rely on the random drawing of a large number of
interactions reproducing the conditions of ionizing traces
possible, following heavy ion interaction or to neutron or proton
nuclear reactions with nuclei constituting the component. They
therefore compute error frequency (SER or Single Event Rate).
[0058] Certain Monte-Carlo prediction codes can be used to take
account of a large number of elementary cells and hence to process
the problems related to multiple effects that appear simultaneously
in different cells of the component.
[0059] The setting up of a Monte-Carlo method consists in managing
three sets of issues and problems:
[0060] 1--Management of the Monte-Carlo draw of interactions as a
function of the environment considered;
[0061] 2--Physics of particle/matter interaction (data bases):
knowledge of the characteristics of the primary ions or of the
secondary ions produced by the neutron or proton reactions with the
constituent nuclei of the components;
[0062] 3--Error criterion: determining the collection of the
charges and their consequence.
[0063] To study the singular effects induced in electronic
components by atmospheric neutrons or protons of radiation belts,
it is necessary to know the ionizing products (known as secondary
ions, recoil nuclei, spallation fragments or products) which these
nucleons prompt with the atoms of the target.
[0064] Given the energy extent or range (1 MeV to 1 GeV) of the
different types of interaction (elastic, non-elastic etc),
different codes have been used to generate data bases in order to
describe the different mechanisms of interaction according to their
specificities, i.e. types of reactions and energies. Dedicated
computation codes such as the HETC, MC-RED, MC-Recoil, GEANT4,
GNASH, or MCNP 6 (depending on the energy of the incident
particles) or data bases of the interaction such as ENDF or JENDL
can be used. Most of these nuclear codes are accessible through the
Internet. The principle of the interaction of a neutron n or a
proton p with a target nucleus is symbolized in FIG. 2.
[0065] For neutron/proton energy levels below 10 MeV, the elastic
reactions are preponderant. Conversely, for energy levels above 50
MeV, reactions of the non-elastic type are in the majority. The
elastic type reactions are those inducing energy from the incident
n/p and a recoil ion (conservation of kinetic energy and of the
mass number). The non-elastic reactions are varied; each reaction
is characterized by an energy appearance threshold. These reactions
induce the generation of one or more secondary ions.
[0066] The data bases process the neutron/matter or proton/matter
interactions and are formed, for each incident energy value, by
hundreds of thousands of non-elastic and elastic nuclear events
with the detail of the nuclear reactions, i.e. the nuclear numbers
and mass numbers of the secondary ions, their energy values and
their sending characteristics (sending angles).
[0067] The general principle of a Monte-Carlo code for the
prediction of sensitivity of electronic components is illustrated
in FIG. 3. The method is that of obtaining a set of random draws of
nuclear reactions associated with a draw of their location in the
component. The making of this set of draws is likened to a duration
of experiment. For each of these configurations, an analysis based
on a simplified model of the study of the physical charge
collection mechanisms makes it possible to decide on the occurrence
of an error induced by secondary ions having such a characteristic.
In the case of the study of heavy ions, the method remains
identical but there is no random drawing of nuclear reactions since
it is only one primary particle that is studied.
[0068] As the case may be, these simulation codes take account of
the size of the ionization trace of the charged particles. Instead
of depositing the charge at only one point, a radial distribution
of the charge is introduced.
[0069] The simplification of the physical module is obtained
through the study of a large number of constituent simulations.
These simulations make it possible, for a given and preliminarily
meshed structure, to resolve the equations of the semiconductor for
each meshing point of the structure and also for each instant of
the time domain studied. These simulations enable a very precise
study of the behavior that an electronic component will have
relative to an ionizing interaction. However, these simulations are
very costly in computation time. For this reason, in the context of
the disclosed embodiments, it is necessary to simplify the method
for simulating the cases of dysfunctioning studied. It is through
the preliminary study of a large number of constituent simulations
that it is possible to identify the parameters influencing the
appearance of the error and define the simplified modules of the
physical mechanisms brought into play which will be implemented in
the prediction tool.
[0070] Thus for example, and without thereby restricting the type
of component to which the disclosed embodiments can be applied, it
is known especially that, in the case of a switching of an SRAM
cell, its sensitivity is characterized by the critical LET
parameter (defined as the loss of energy per path unit) or critical
charge. For an error to be prompted, the ion or ions generated by
the nuclear reaction must deposit sufficient energy in the drains
of the transistors in the OFF state. Component simulations have
shown that conditions favorable to the creation of an error make
its trace pass fairly close to one of the sensitive zones, or else
goes through it so as to induce therein a parasitic current or a
collection of charges sufficient to create a switching. Simple
diffusion-collection models (especially analytical models) based on
ambipolar diffusion of the carriers and the collection of the
charges at the blocked drains make it possible to describe the
shifting of the carriers.
[0071] Various methods can be used to assess whether or not the
dysfunctioning that follows the passage of an ion has occurred. The
first method entails a simplified approach (of the first order). It
is based on the determining of the charge deposited by the ion in
the sensitive volume of the elementary cell and of the comparison
of this cell with a threshold switching value.
[0072] The second method is a finer study of the phenomenon (second
order phenomenon). In FIG. 4a, the collection of the carriers
deposited by the passage of the ion is studied temporally in order
to rebuild the current. The temporal progress of the current is
used to determine whether or not a switching is occurring. For
example the dynamic criterion (Imax, tImax) introduces a borderline
curve separating the pairs (Imax, tImax) inducing switchings also
called SEU (Single Event Upsets) from those which do not induce any
such switching. Starting from the observation that all the passages
of particles induce currents which have the same shape i.e. prompt
growth followed by slow decrease, each passage of an ion can be
characterized by the pair constituting a maximum amplitude of the
current (Imax) and the time at which it is set up (tImax).
[0073] FIG. 4b shows the example of the principle of the dynamic
criterion (Imax, tImax) to study the sensitivity to SEUs for a 0.6
.mu.m technology. To measure the malfunction of the component, we
measure the progress in time of the current resulting from the
excitation. The criterion (Imax, tImax) of this current makes it
possible to decide on the switching of the logic state of the
component.
[0074] The above-mentioned examples pertain to the study of the SEU
mechanism in an SRAM memory cell but one aspect of the disclosed
embodiments can be applied to any type of electronic component and
any type of effect induced by radiation provided that the criterion
of the effect induced by radiation is identified (since a same
criterion can be common to several effects induced by the
radiation).
[0075] In addition to the nuclear data base described here above,
curves are provided by a computation code (such as for example the
SRIM tool accessible through the Internet) describing the behavior
of the energy deposit of the secondary ions or the heavy ions
during their passage into the material. The data base and the SRIM
curves are fixed whatever the type of errors studied but depend on
materials which constitute the electronic component. The
technological inputs needed for the computation code are the
information on the topology of the component (i.e. the volume of
the sensitive zones and the distance between two sensitive zones).
These parameters vary according to the component and the type of
errors studied.
[0076] The inputs needed to predict sensitivity of an electronic
component are: the dimensions of an elementary cell, the dimension
and position of the sensitive volume of a cell associated with the
desired phenomenon and the positions of the neighboring sensitivity
zones. The laser tool is used to obtain this information. The
coupling between the prediction tool and the laser mapping makes it
possible therefore to quantify the sensitivity and quality of the
electronic components. The processing if any of the information
obtained by the laser mapping depends on the level of integration
of the component relative to the sizes of the laser spot and the
ionization traces of the particles brought into play. This
geometrical data is used at input of the prediction codes to
quantify the sensitivity of an electronic component relative to the
particles of the natural radiating environment.
* * * * *